The operation of gas turbine plants, and especially of their compressors, is accompanied by considerable sound emissions. Therefore, the air inlet ducts to the compressors are equipped with different devices for silencing.
A sound damper, or “silencer”, in an air inlet duct to a compressor for a gas turbine plant is disclosed for example in U.S. Pat. No. 6,260,658. The silencer is arranged in the front horizontally disposed region of the inlet-duct, and perpendicular to the flow direction of the incoming air, across the entire cross section of the inlet duct. It comprises a plurality of damper units which extend in parallel and are spaced apart by means of interspaces, wherein the inducted air flows through the interspaces. The damper units contain sound-absorbing material consisting of foam, wool, mineral wool, fiberglass or basalt wool.
A further system for silencing in a turbomachine is known from U.S. Pat. No. 5,709,529. It comprises a combination of curved baffle plates which extend parallel to one another and are arranged in a bend of an inlet duct, and a sound-absorbing lining of the inner walls of an inlet chamber directly upstream of the inlet to the turbomachine. In this case, the curved baffle plates are arranged at specific distances from one another according to the bend radius of the air inlet duct. The system achieves the effect of so-called “spinning mode tone harmonics” which occur in turbomachines, especially in aircraft engines, as a result of the interaction of rotor and stator blades of the turbomachine, being toned out. For this purpose the sound-damping lining is oriented perpendicularly to the direction of motion of the “spinning mode tones”. The lining for example consists of mineral wool, fibreglass or ceramic fibers.
In the air inlet duct to the compressor of a gas turbine plant, considerable moisture often occurs, especially when using “fogging” methods, that is by specific wetting of the air for the purpose of more efficient operation of the gas turbine plant. Furthermore, the components of the air inlet duct are loaded with SO2, salts and other aggressive chemical substances. The use of the described silencing devices in air inlet ducts, which are chemically loaded and/or loaded with moisture, would lose effectiveness on account of their material selection, since on the one hand the sound-damping action is reduced, and on the other hand the materials would degrade. Glass fibers in particular lose their capability for sound damping in the event of moisture, while mineral wool, rock wool and also polyurethane foam are not materially resistant in the case of attack by salts or sulphur dioxide.